I'm not the best person on n2100 specific issues, but I can make some
more general comments.

It's a pretty classic "error" to use apt-get -f and then find you need
to do a large scale mend. See it more as a learning opportunity! It
does make me cautious about advising you on the basis of what I
personally would do next, because you do have to be a bit careful when
doing more adventurous things on debian (or in most other contexts!) as
you've found.

First and major point: if you can back up your data, do so now or soon.
I should have thought your options in order of preference were:

(1) stick with lenny, and fix the samba shares. You get to keep the
"piece of software" you wanted (could you live without it if you went
back to etch?) and lenny is good, with occasional glitches if you do
keep upgrading. Can you not make out from smb.conf and its fellows why
you can't now see the missing shares? Samba is a notorious pig, but
simple configuration is usually straightforward and moderately
transparent. Personally, I've used (debian) swat as a GUI samba
configuring tool with some success: if you do use swat, make a backup of
your smb.conf first, as swat prunes and rewrites it drastically (and
much more simply).

(2) re-install etch, while keeping your data partitions. Judging by
your previous posts, you used the debian installer, and I presume that
involved using the installer's partitioner. These days, the partitioner
is just superb (IMHO - I have no involvement other than as a very
satisfied user). You may recall using it: you should be able to tell it
to mount the existing data partitions where you are used to seeing them,
and to preserve the data on them. Just make sure you follow the
partitioner carefully, and watch out especially when it says it's about
to (when you press the Yes button) repartition, or create new (blank)
filesystems - make sure these are on the bits of the disk you do want
blanked. The main disadvantage of this option, as far as I can see, is
that you'll have to set up the samba stuff again (do keep a copy of
smb.conf before you start!) and if you're having trouble in the current
lenny, mightn't you have trouble again? That's the main reason I
suggest trying (1) first.

(3) (not very serious) do what mad people like me might do: use
debootstrap from your lenny to create a new etch install on a spare part
of your disk(s) (ideally an lvm2 logical volume), and get it working
while keeping the lenny install as a fallback if/when things go wrong.

I can't speak with any knowledge to the question about reverting to the
thecus rom, but I doubt (from my NSLU2 experience) that's necessary.

Hope this is some help!
Barry

PS I wonder how you access your debian from Windows? ssh (eg PuTTY) is
standard and good, but with a little learning, Xming is quiet superb
(once you install xorg on the debian side) and gives you access to
almost all the gui stuff in debian from your windows desktop.